Self-affine fractal vapour-deposited gold surfaces characterization by scanning tunnelling microscopy

The morphological evolution of the surfaces of gold deposits grown from the vapour on smooth glass under nonequilibrium conditions and incident angle near substrate normal is studied at the nanometer level by scanning tunnelling microscopy. For an average film thickness equal to or greater than 500 nm, the interface thickness (ξ) reaches a steady state. Under these conditions, ξ depends on the scan length (L) as ξ ∝ Lα with α = 0.35 ± 0.05 for L > ds, where ds is the columnar size, and α = 0.89 ± 0.05 for L s. These results indicate that the growing surface spontaneously reaches a steady state and it can be described as a self-affine fractal. The value of α for L > ds agrees with the prediction of ballistic deposition models without restructuring, whereas that for L s exceeds the prediction of ballistic models including restructuring.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Self-affine fractal electrodeposited gold surfaces: Characterization by scanning tunneling microscopy

The morphological evolution of columnar gold electrodeposits grown at 100 nm s −1 by electroreducing a gold oxide layer on a gold cathode has been studied at a nanometer level by scanning tunneling microscopy. The interface thickness (ξ) depends on the scan length (L) as ξ∝ L α with α=0.49±0.07 for L > ds, where ds is the average top columnar size, and α=0.90±0.07 for L s. These results prove that the growing surface can be described as a self-affine fractal for length scales greater than the columnar size. Conversely, the columnar surface approaches the behavior of an Euclidean surface.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Self-affine fractal electrodeposited gold surfaces: Characterization by scanning tunneling microscopy

The morphological evolution of columnar gold electrodeposits grown at 100 nm s −1 by electroreducing a gold oxide layer on a gold cathode has been studied at a nanometer level by scanning tunneling microscopy. The interface thickness (ξ) depends on the scan length (L) as ξ∝ L α with α=0.49±0.07 for L > ds, where ds is the average top columnar size, and α=0.90±0.07 for L s. These results prove that the growing surface can be described as a self-affine fractal for length scales greater than the columnar size. Conversely, the columnar surface approaches the behavior of an Euclidean surface.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Self-affine fractal vapour-deposited gold surfaces characterization by scanning tunnelling microscopy

The morphological evolution of the surfaces of gold deposits grown from the vapour on smooth glass under nonequilibrium conditions and incident angle near substrate normal is studied at the nanometer level by scanning tunnelling microscopy. For an average film thickness equal to or greater than 500 nm, the interface thickness (ξ) reaches a steady state. Under these conditions, ξ depends on the scan length (L) as ξ ∝ Lα with α = 0.35 ± 0.05 for L > ds, where ds is the columnar size, and α = 0.89 ± 0.05 for L s. These results indicate that the growing surface spontaneously reaches a steady state and it can be described as a self-affine fractal. The value of α for L > ds agrees with the prediction of ballistic deposition models without restructuring, whereas that for L s exceeds the prediction of ballistic models including restructuring.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

A comparative study of electrodeposited and vapour deposited gold films : Fractal surface characterization through scanning tunnelling microscopy

The surfaces of Au deposits grown under non-equilibrium conditions from either the electroreduction of Au oxide or from the vapour have been analysed as fractals by measuring the perimeter (P) and the area (A) of intergranular voids. The values of P and A were determined from scanning tunnelling microscopy (STM) topographic imaging of the deposit surfaces. A frsctal behaviour P ∝ 4 D/2 was found with D = 1.5 ± 0.1 and D = 1.7 ± 0.1 for the electrodeposited and vapour deposited Au iilms, respectively. These figures remain constant for film thicknesses between 100 and 1000 mn. The value of D, the fractal dimension of the surfaces, is 2.5 ± 0.1 for the Au electrodeposits, and 2.7 + 0.1 for the Au vapour deposited films. The former value is consistent with either a diffusion or an electric field controlled growth model, whereas the latter is in agreement with a ballistic growth model.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Methods of fractal analysis applied to STM imaging

Vapor deposited gold films have been characterized by applying methods of fractal analysis to scanning tunneling microscopy (STM) images. Results from the use of five different methods are in agreement within the limitation of each method. Those methods are suitable to characterize rough surfaces at the nanometer level provided that a large number of images is considered.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Scanning Tunneling Microscopy Fractal Characterization of Poly (o-toluidine) Films Produced Electrochemically on Polyfaceted Gold Single Crystal Spheres

The topography evolution of a poly(o-toluidine) layer (the object) electrodeposited on a polyfaceted Au single crystal from 0.5 M H2SO4 + 0.65 M o-toluidine aqueous solution at 25 °C has been studied combining nanometer scale ex-situ scanning tunneling microscopy and electrochemical techniques. A thin polymer layer structure consists of nodular elements following the substrate topography, whereas a thick polymer structure corresponds to a rather disordered structure made up of agglomerates formed by nodular elements with average diameter size ds ≅ 15 nm. In contrast to the former one, this structure is independent of the substrate topography. For thick layers ξ, the root-mean-square roughness of the polymer coating, and Ls, the scan length, fulfill a ξ ∝ Lα relationship with a = 0.33 ± 0.05 for Ls > ds and α = 0.85 ± 0.05 for Ls s- Accordingly, the polymer layer surface behaves as a self-affine fractal. For Ls s the value of a agrees with that predicted for moving interfaces generated by the Eden model, whereas for Ls s the value of a approaches that expected from an Euclidean surface. The topographic analysis of these polymer layers can be related to the kinetics of electrochemical reactions at polymer-coated Au electrodes.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Self-affine fractal electrodeposited gold surfaces : Characterization by scanning tunneling microscopy

The morphological evolution of columnar gold electrodeposits grown at 100 nm s −1 by electroreducing a gold oxide layer on a gold cathode has been studied at a nanometer level by scanning tunneling microscopy. The interface thickness (ξ) depends on the scan length (L) as ξ∝ L α with α=0.49±0.07 for L > ds, where ds is the average top columnar size, and α=0.90±0.07 for L s. These results prove that the growing surface can be described as a self-affine fractal for length scales greater than the columnar size. Conversely, the columnar surface approaches the behavior of an Euclidean surface.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Scale-dependent roughening kinetics in vapor deposited gold

The roughening kinetics of gold deposits grown from vapor was studied by scanning tunneling microscopy. The dynamic scaling yielded the following growth exponents α(I)=0.90±0.06 and β(I)=0.25±0.06 for Ls>ds, and α(II)=0.37±0.05 and β(II)=0.45±0.06 for Ls>ds, where Ls is the scan length and ds is the average diameter of columns. The scaling properties of the domain-dependent-surface roughness exponents allowed us to give the rationale for experimental data on the fractal behavior of thin metal films.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

STM study of fractal scaling in evaporated gold films

Fractal characterization of vacuum-evaporated gold films on glass substrates with thicknesses (h) comprised between 30 and 850 nm is made from STM data by using the dynamic scaling approach for surface growth. The rms roughness (ξ) and the scan length (L) obey a ξ versus Lα relationship with α depending on h. For h ⪰ 500 nm and L >ds, the averag e column diameter, α≌13 in agreement with the predictions of ballistic deposition models without restructing. For L s, α ≌ 0.9 approaching a euclidean value. The STM method is verified through its application to several computer-generated surfaces, leading to a good agreement with the theoretical values.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada